Transformers

[garfield at pilgrimhouse.com]

On Thu, 28 May 1998 16:21:56 -0400, kenkelly at lucent.com wrote:

>Bruce,
>	When you talk about a points ignition you use the coil in a
>different mode than a CDI. In the points ignition you
>saturate the coil core magnetically. When the points open
>the field collapses and generates the spark. In the CDI
>ignition you apply a short ~300 Volt pulse to the coil and
>use it as a stepup transformer to create the spark pulse.
>
>		Ken

Yup, nice precise concise. And whether you have points, or a pickup
running a module, they both basically do the same thing described above;
namely they switch on to conduct current throught the primary until the
coil primary is saturated, and then switch off/open the connection to
fire the spark. I dunno exactly why someone first decided to call the
"saturated coil" type of IGN, "inductive" IGN, cuz both schemes use
magnetic induction fundamentally, but Bruce the reason why CDI is called
"capacitive discharge" is that the short ~300-400V pulse Ken is refering
to is created in the primary of the coil by "dumping" a capacitor that's
already been charged up to that voltage, into the primary. Usually this
is done with a FET or SCR or some kinda switching device that abruptly
connects the charged capacitor across the primary. The capacitor
discharging into the coil primary and producing this pulse, is where the
name CDI comes from.

Gar